The sterol pathway in yeasts involves many steps. A diagram of the yeast sterol pathway is presented as FIG. 14, and reference is made to it discussing prior art, below.
U.S. Pat. No. 5,460,949 (Amoco) teaches a method and composition for increasing the accumulation of squalene and trienol in yeast. This method includes truncation and over-expression of HMG1 (the single most important gene regulating the pathway) in a strain in which the genes ERG5 and ERG6 are inactivated. ERG5 and ERG6 encode the two enzymes activities that distinguish ergosterol, which is the major sterol of yeast and fungi, from cholesterol biosynthesis. These strains preferably accumulate cholesta-5,7,24-trienol, which is usually an intermediate of cholesterol biosynthesis.
WO03/064650 (Lang et al) (US2006/0240508) discloses a method for the production of 7-dehydrocholesterol and/or the biosynthetic intermediate or subsequent products in yeast. Here, the genes for the C-8 sterol isomerase, the C-5 sterol desaturase, and the sterol Δ24-reductase from mouse and human were expressed in a yeast strain in which ERG5 and ERG6 were inactivated and the HMG1 gene was truncated and overexpressed. These yeasts were able to synthesize 7-dehydrocholesterol.
WO03/064652 (Lang et al) (US2006/0088903) discloses a method for the production of zymosterol and/or the biosynthetic intermediate and/or subsequent products thereof in transgenic yeast by increasing lanosterol-C14-demethylase activity (ERG11).
WO 2005/121315 (Aventis) teaches cholesterol-producing yeast strains and uses thereof. A sterol Δ7 reductase gene from Arabidopsis thaliana and a human sterol Δ24-reductase gene were introduced into various yeast host strains in which ERG6 and, in some cases, ERG5 were inactivated. The new strains were able to produce cholesterol in admixture with other intermediates.
U.S. Pat. No. 6,562,609 (Russell et al) teaches an isolated human and mouse cholesterol C25-hydroxylase and genes.
The prior art is silent as to production of 25-hydroxyprovitamin D3 or 25-hydroxyprovitamin D2 using transgenic yeast.